Metallic containers are frequently decorated with an image or indicia, such as a brand name, logo, product information, or design, using a lithographic printing process. In lithographic printing, one or more printing plates with image regions are attached to a plate cylinder (or press cylinder) of a decorator. The image regions can include both ink receiving regions and areas that do not receive ink. An inker applies ink to the printing plates and the ink adheres to the ink receiving regions. Usually each printing plate receives a particular color of ink from the inker. The decorator also has a blanket cylinder (also known as an offset cylinder, a printing cylinder, or a segment wheel). Printing blankets (or secondary transfer plates) are attached to the blanked cylinder. Decorators used in the metallic container industry typically have from 8 to 12 printing blankets on the blanket cylinder. As the plate cylinder and blanket cylinder are rotated in unison, each of the one or more printing plates contacts a printing blanket and transfers a particular color of ink to the printing blanket. When all of the printing plates have transferred their ink colors and images to the printing blanket, the final lithographic image is formed on the printing blanket. A metallic container is then brought into rotational contact with the printing blanket of the blanket cylinder and the lithographic image is transferred from the printing blanket to the exterior surface of the metallic container.
Lithographic printing methods are described in U.S. Pat. No. 4,384,518, U.S. Pat. No. 6,550,389, and U.S. Pat. No. 6,899,998, which are each incorporated herein by reference in their entireties. The methods described in these references only allow a single lithographic image to be produced from a single set of printing plates. Therefore, the methods described in these patents are only efficient for printing the same image onto a large number of metallic containers. In order to print a different image on the metallic containers, a new set of printing plates must be installed on the plate cylinder of the decorator, resulting in downtime and decreased efficiency of a production line. Because only one image can be printed without changing the printing plates, it is economically challenging to produce small batches of decorated metallic containers with different images.
One example of providing multiple images from a single set of printing plates is provided in International Patent Publication No. WO 2014/008544, which is herein incorporated by reference in its entirety. This reference describes a blanket cylinder with printing blankets that are adapted to have inked regions and non-inked regions. The non-inked regions are recessed inwardly and are formed by laser cutting, etching, water blasting, routing, drilling, engraving, or molding. However, lithographic images produced by the non-inked regions formed on the printing blankets using these techniques do not have enough detail to be considered a high quality, high-definition image. The commercial metallic container industry requires high-definition printing in unique applications and requires distinct graphical elements that can efficiently be printed with high resolution and detail on the exterior surface of a metallic container. These high-definition images are necessary to differentiate products at the point of sale and to attract consumers.
Accordingly, there is an unmet need for a high-definition lithographic printing process that allows multiple images to be printed on an exterior surface of a metal container from a single set of printing plates without sacrificing production efficiency or image quality and detail.